Method for detecting a contour of a given subject to be separated from images and apparatus for separating a given subject from images

Abstract

A method for detecting a contour of a given subject to be separated from images utilizing an image separating system. First, a plurality of candidate points which have been input by a user are displayed on a screen. A smooth curve which connects the plurality of candidate points is determined and is displayed on a display apparatus. The intensity of light on a straight line extending in a direction normal to each candidate point is determined. The position of the candidate point is corrected based upon the rate of change in the intensity of light which is determined for each candidate point. A smooth curve which passes the corrected candidate points is determined and is displayed on the display apparatus. The specified image, represented by the smooth curve connecting the corrected candidate points, is then separated from the rest of the image elements.

We claim: 
     
       1. A method for detecting image separating points where only a given subject image is separated from images, said method comprising the steps of: a first step for displaying on a screen a plurality of candidate points in the vicinity of a boundary of said given subject image, which are input by a user;   a second step for determining and displaying a smooth curve which connects said plurality of candidate points;   a third step for determining a rate of change in intensity of each of a plurality of light components of said image having different wavelengths along a straight line normal to said curve at each of said plurality of candidate points;   a fourth step for correcting the position of each of said candidate points, respectively, by calculating a corrected position for each of said plurality of candidate points based upon the rate of change in intensity of light determined at each of said plurality of light components of said plurality of candidate points;   the calculation of the corrected position of each of said plurality of candidate points includes determining a preliminary corrected point for each of said plurality of light components of each of said plurality of candidate points based on the rate of change in intensity of each of said plurality of light components; and   a fifth step for determining and displaying a smooth curve connecting said corrected candidate points.   
     
     
       2. A method for detecting image separating points according to claim 1, wherein when at least two of said preliminary corrected points are within a predetermined distance of each other, the corrected position of the corresponding candidate point is determined to be the average of the coordinates of the at least two preliminary corrected points,   when none of said preliminary corrected points are within a predetermined distance of each other, no corrected position of the corresponding candidate points is determined to exist, and the corresponding candidate point is used as the corrected candidate point,   when only one preliminary corrected point is determined to exist for any one of said plurality of light components of said plurality of candidate points, the one preliminary corrected point is used as the corrected candidate point, and   when no preliminary corrected point is determined to exist for any of said plurality of light components of said plurality of candidate points, the corresponding candidate point is used as the corrected candidate point.   
     
     
       3. A method for detecting image separating points according to claim 1 wherein, when the rate of change in the intensity of each of said plurality of light components is determined in said third step, designated values of threshold parameters for determining the rate of change in intensity of each of said plurality of light components for detecting an edge shape of said subject image are changed. 
     
     
       4. A method for detecting image separating points according to claim 1 wherein, when a smooth curve connecting the plurality of candidate points is determined in said second step, the position of at least one of said candidate points is preliminarily designated as a fixed point for which there is no processing in said third and fourth steps, while processing of the second to fifth steps is performed for all of the remaining candidate points. 
     
     
       5. A method for detecting image separating points according to claim 1 wherein, in said third step, processing for determining said rate of change in the intensity of each of said plurality of light components is sequentially performed from the external to internal slide along the straight line normal to said curve at each of said candidate points on said curve traced in the vicinity of the contour of the subject, and a point which satisfies conditional formulae representing that the rate of change for correcting said plurality of candidate points is higher than the threshold is determined as the position of a preliminary corrected point. 
     
     
       6. A method for detecting image separating points according to claim 5 wherein, after processing of said fifth step, said threshold of said rate of change is changed for at least one of said candidate points which are determined as not satisfying said conditional formulae as a result of the determination of said rate of change in intensity of each of said plurality of light components in said fourth step, and then processing of said third to fifth steps is repeated at least once for said at least one candidate point. 
     
     
       7. A method for detecting image separating points according to claim 5, further including steps of determining a candidate point input in the first step to be the position of the corrected candidate point, and adding to said candidate point an attribute representing that it does not satisfy the conditional formulae for correcting the position, including displaying said candidate point in a color different from that of the other point on the screen. 
     
     
       8. A method for detecting image separating points according to claim 5, further including the steps of determining a candidate point input in the fourth step to be the position of the corrected candidate point, and adding to said candidate point an attribute representing that it satisfies the conditional formulae for correcting the position, including displaying said candidate point in a color different from that of the other point on the screen. 
     
     
       9. A method for detecting image separating points according to claim 1 wherein, if processing is repeated again from the second step after completion of said fifth step, at least one candidate point is designated as a fixed point for which there is no processing in said third and fourth steps, and each processing of the third, fourth and fifth steps is repeated at least once from a point adjacent to said fixed point for all of the remaining candidate points. 
     
     
       10. A method according to claim 2, wherein said predetermined distance is variable. 
     
     
       11. An apparatus for detecting image separating points where only a given subject image is separated from images, said apparatus comprising: first means for displaying on a screen a plurality of candidate points in the vicinity of a boundary of said given subject image, which are input by a user;   second means for determining and displaying a smooth curve which connects said plurality of candidate points;   third means for determining a rate of change in intensity of each of a plurality of light components of said image having different wavelengths along a straight line normal to said curve at each of said plurality of candidate points;   fourth means for correcting the position of each of said candidate points, respectively, by calculating a corrected position for each of said plurality of candidate points based upon the rate of change in intensity of light determined at each of said plurality of light components of said plurality of candidate points,   said fourth means including means for determining a preliminarily corrected point for each of said plurality of light components of each of said plurality of candidate points based on the rate of change in intensity of each of said plurality of light components; and   fifth means for determining and displaying a smooth curve connecting said corrected candidate points.